受约束早龄期混凝土收缩开裂的理论预测和试验研究

金南国，金贤玉，田野为了揭示受约束混凝土内部的应力发展以及更好地预测混凝土的开裂时间，研究了纤维对高性能混凝土早龄期力学性能与干燥收缩的影响，考虑徐变、约束度等影响因素，在弹性理论基础上，推导了受约束混凝土环应力增量表达式，采用应力破坏准则预测受约束混凝土开裂时间.研究结果表明，在特定的配合比下，掺加聚丙烯腈纤维使混凝土各龄期的干燥收缩应变降低2％～20％，且降低幅度随着龄期的增加而减小；掺加聚丙烯腈纤维可以延迟混凝土的开裂时间，减小裂缝宽度.针对受约束混凝土环，理论预测掺纤维与未掺纤维混凝土的开裂时间分别为28和22 d，理论预测结果与试验结果吻合良好.

Analytical prediction and experimental research on shrinkage cracking of restrained early-age concrete

The early-age mechanical properties and drying shrinkage of high performance concrete added with fiber were studied to investigate the development of stress in restrained concrete and predict the cracking age of concrete more precisely. An incremental representation of stress of restrained concrete ring was established based on elasticity theory in considering creep and restraint degree. Then the maximum tension stress theory was introduced to predict the cracking age of restrained concrete ring. Experimental and theoretical analysis showed that fiber addition reduced the drying shrinkage for about 2% to 20% at different ages, and the reduction decreased with age. Fiber addition also postponed the cracking age of concrete ring and narrowed the crack width. In theory, the cracking ages of the high performance concrete with and without fiber were 28 and 22 d respectively, which were in good agreement with the experimental results.